Using the `Card` class

Using the Card class

Look only at the public things in the Card class:

public class Card { public static final int SPADE = 4; public static final int HEART = 3; public static final int CLUB = 2; public static final int DIAMOND = 1; public Card( int suit, int rank ) ... public int suit() ... public String suitStr() ... public int rank() ... public String rankStr() ... public String toString() ... }

From the definitions of the public methods, we can tell how to use them

The constant value SPADE:

Because the definition contains the keyword static:

public static final int SPADE ....

it is a class constant and the syntax used to refer to SPACE is:

Card.SPADE

Other constants are used in a similar fashion.

The constructor Card( int suit, int rank):

We know that a constructor is used to initialized a newly created Card object
From its definition, we know this particular constructor takes 2 int parameters

Example usage:

Card x; x = new Card( Card.CLUB, 1 ); // Ace of club

Note:

The method int suit()

We know that it is an instance method
(Because it does not have the keyword static

Therefore, the suit() method must be invoked using an object variable, like this:

Card x; x = new Card( Card.CLUB , 1 ); x.suit() // (suit() has no parameters)

Because the method suit() returns an int value, we need to stored the return value in an int typed variable:

Card x; int r; x = new Card( Card.CLUB , 1 ); r = x.suit() // (suit() has no parameters)

The above discussion also applies to the other instance methods (because they are similar).

Example Java program showing how to use the Card class:

public class TestCard1 { public static void main(String[] args) { Card x; int r; String s; x = new Card( Card.CLUB, 1); // Create a card r = x.suit(); // Get the suit of a card System.out.println("x.suit() = " + r); r = x.rank(); // Get the rank of a card System.out.println("x.rank() = " + r); s = x.suitStr(); // Get the suit of a card (Str) System.out.println("x.suitStr() = " + s); s = x.rankStr(); // Get the rank of a card (Str) System.out.println("x.rankStr() = " + s); System.out.println(x.toString()); // Convert a card into a String System.out.println(x); // toString() invoked automatically // by Java to convert object to String!!! } }

Output:

x.suit() = 2 (2 = club) x.rank() = 14 (rank of Ace) x.suitStr() = c (club) x.rankStr() = A (Ace) Ac Ac

Example Program: (Demo above code)
- The Card.java Prog file: click here
- The TestCard1.java Prog file: click here
How to run the program:

What is going on behind the scene in the above example

This is what is going on behind the scene:

The variable definitions in main() first create the local variables:
The new Card operator first create a Card object and returns a object reference to the local variable x:
Immediately, the execuition will invoke the constructor using the newly created object
In other words:

This is what happens inside the execution of the constructor method:

The parameters (x, Card.CLUB and 1) are passed to the constructor method:
The assignment cardRank = 14 (is short hand for this.cardRank = 14), will store the value 14 into the instance variable cardRank:
The assignment cardSuit = suit (is short hand for this.cardSuit = suit), will store the value 2 into the instance variable cardSuit:
When the constructor exits, we have
initialized the newly created object:

Invoking of the instance method x.suit() is executed as follows:

The invocation will pass x as the implicit parameter this:
The instance method will now use the implicit parameter this to return the cardSuit (= 2) value:
because return(cardSuit) is the short hand for return(this.cardSuit)

Using the Card class

Using the `Card` class